Fuel economy is of great concern among operators of fleets of vehicles, particularly trucks used for hauling loads over a wide range of speeds on highways. The truck driver interested in maximizing fuel economy can be particularly aided by a continual display of the current fuel economy of the truck. The truck driver can use this information to develop and maintain driving habits which maximize fuel economy.
It has been known to use the manifold vacuum of an internal combustion engine propelling a vehicle to serve as an indicator of the fuel economy being achieved by that vehicle. Manifold vacuum is, however, a highly erratic variable and is dependent upon outside conditions such as atmospheric pressure. For these reasons, manifold vacuum does not provide an accurate or stable reading, greatly reducing its value as an indicator of engine fuel economy.
It has also long been known in the art to measure the engine fuel consumption rate and speed of the vehicle to calculate an instantaneous measure of fuel economy. These instantaneous measures of fuel economy are also highly erratic, but can be smoothed by means of electronic signal processing to produce a more stable and usable measure of fuel economy.
In U.S. Pat. No. 4,354,173, issued to Kuhn et al., an apparatus for indicating the fuel economy of a motor vehicle includes sensors for detecting engine speed, distances travelled by the vehicle, and the engine throttle. In addition, an accelerometer is coupled to the distance sensor to determine the vehicle acceleration. The signals from these sensors are combined to produce a signal indicative of the fuel economy of the vehicle and useful to alert the vehicle operator when, for example, the vehicle's transmission should be shifted.
In U.S. Pat. No. 4,113,046, Arpino discloses of a method and an apparatus for indicating the fuel economy of a vehicle during acceleration. The apparatus uses a throttle rate signal in combination with an acceleration signal to generate an efficiency signal. This efficiency signal drives an indicator to show whether the vehicle is accelerating efficiently. The efficiency signal can also be used in a vehicle speed control device to automatically control the acceleration of the vehicle.
The prior art does not disclose a fuel economy measurement system which accounts for changes in the fuel economy that are due to changes in the vehicle's kinetic energy as the vehicle acelerates or decelerates. Therefore, fuel economy indication systems that do not account for changes in the kinetic energy produce misleading signals whose behavior can be annoying to a driver who is attempting to maximize fuel economy.
The present invention provides an apparatus for correcting fuel economy measurements to account for changes in the kinetic energy og the vehicle. This apparatus is extremely simple and does not require sensors to measure throttle position, rate of change of throttle position, or vehicle acceleration.